1. Field of the Invention
The present invention relates to a microchannel apparatus for producing emulsions used in the food industry, the manufacturing of drugs and cosmetics, etc., and to a method of producing emulsions making use thereof.
2. Description of Related Art
Techniques in which a biphasic system, for which a separated state is thermodynamically stable, is formed, such as that composed of a water phase and an organic phase which are emulsified to obtain a semi-stable emulsion, are conventionally known. As general emulsification methods, there have been described in "Science of Emulsions" (Asakura-shoten, 1971), the methods of using a mixer, a colloid mill, a homogenizer, etc., and the method of dispersion with sound waves, which are all well-known.
The general methods mentioned above have a disadvantage in that diameters of dispersed phase particles in a continuous phase are distributed over a wide range.
Therefore, a method of using filtration by means of a membrane comprising polycarbonate (Biochemica et Biophysica Acta, 557 (1979), North Holland Biochemical Press); a method using repeated filtrations through a PTFE (polytetrafluoroethylene) membrane (Proceedings of the 26th Autumn Meeting of the Society of Chemical Engineers, Japan, 1993); and, a method of manufacturing homogenous emulsions by transferring a dispersed phase into a continuous phase through a porous glass membrane having uniform pores (Japanese Patent Application Laid-Open No. 2-95433), have been proposed.
As a method of producing emulsions using a nozzle or a porous plate, a laminar-flow dripping method (KAGAKU KOOGAKU Vol. 21, No. 4, 1957) is also known.
The method using filtration through a membrane comprising polycarbonate and the method using repeated filtrations through a PTFE membrane theoretically cannot manufacture emulsions comprising particles larger than the membrane pores and cannot separate particles smaller than the membrane pores. These methods are, therefore, especially unsuitable for producing emulsions comprising large particles. In addition, these methods using a membrane are unsuitable for industrially mass producing emulsions.
In the method using a porous glass membrane having uniform pores, when the average diameter of the membrane pores is small, particle diameters are distributed in a narrow range and thus homogenous emulsions can be obtained. When the average diameter of the membrane pores is increased, however, particle diameters become distributed over a wide range so that homogenous emulsions cannot be obtained. In addition, in the laminar-flow dripping method, particle sizes become 1,000 .mu.m or more and are distributed over a wide range so that homogenous emulsions cannot be obtained.
Therefore, the inventors of the present invention formerly proposed an apparatus which can produce homogenous emulsions continuously in International Publication No. WO97/30783.
The structure of this apparatus is shown in FIGS. 10 and 11. FIG. 10 is a vertical sectional view of this apparatus and FIG. 11 shows a base and a plate taken apart.
In this apparatus for producing emulsions, a supply port 101 for a continuous phase (W) is formed in a side wall of a body 100, a supply port 103 for a dispersed phase (O) is formed in the center of a lid 102 which closes an upper opening of the body 100, and a withdrawal ports 104 for emulsions (E) are formed at a place apart from the center. A bulkhead member 106 formed between the lid 102 and the base 105 separates the supply port 103 for the dispersed phase (O) from the withdrawal ports 104 for emulsions (E). In addition, a supply port 107 for the dispersed phase (O) is formed in the center part of the base 105, a gap 109 is formed between the base 105 and the plate 108 placed opposite the base 105, a boundary section 110 formed in the base 105 separates the dispersed phase (O) and the continuous phase (W), and via a microchannel 111 formed in the boundary section 110 the dispersed phase (O) and the continuous phase (W) are mixed.
The dispersed phase (O) supplied to the inside of the bulkhead member 106 via the supply port 103 enters the gap 109 between the plate 108 and the base 105 via the supply port 107 and this dispersed phase (O) enters the continuous phase (W) through the microchannels in the boundary section 110, thereby forming emulsions.
In addition, the inventors of the present invention have proposed other microchannel apparatuses, as improvements of the apparatus disclosed in International Publication No. WO97/30783, in Japanese Patent Application Nos. 10-83946 and 10-187345.
In the apparatus proposed in Japanese Patent Application No. 10-83946, emulsions are easily withdrawn by orienting the apparatus shown in FIG. 10 in a vertical direction or inclined and using differences in specific gravity between the dispersed phase and the continuous phase. The apparatus proposed in Japanese Patent Application No. 10-187345 is a cross-flow apparatus which pumps the dispersed phase into the continuous phase continuously flowing from one side and it is very effective for continuously producing emulsions.
FIG. 12 is an enlarged view of the microchannel part of the apparatus disclosed in International Publication No. WO97/30783, as well as in Japanese Patent Application Nos. 10-83946 and 10-187345.
The microchannels 111 are formed between convex portions 112. Because of the differences in size of each microchannel and the positions in which microchannels are formed, the pressure to obtain break-through (i.e. pressure at which production of microspheres starts) differs in each microchannel.
Accordingly, as shown in FIG. 12, of the base, in the case of applying low pressure to the dispersed phase, microspheres (fine particles of dispersed phase) are formed only in one or another specific microchannel, so as to obtain very homogenous microspheres. However, it is unsuitable for mass production because the rest and indeed most of the microchannels do not take part in producing the microspheres.
On the other hand, as shown in FIGS. 13(a) and 13(b), in the case of applying considerably high pressure to the dispersed phase in order to produce microspheres from all microchannels in the previously proposed apparatus, to make mass production more efficient, adjacent microspheres connect and unite with each other, so as to grow large.